如果我对于 $m > n$ 的情况将列按最大值排序，再将前n列复制到新数组中，$m <= n$ 直接复制到新数组中，like this：

for (int i = 1; i <= m; i ++ ) w[i].second = i;
		for (int i = 1; i <= n; i ++ ) 
			for (int j = 1; j <= m; j ++ ) 
				cin >> a[i][j], w[j].first = max(w[j].first, a[i][j]);
		sort (w + 1, w + m + 1, cmp);
		
		if (m > n) {
			m = n;
			for (int i = 1; i <= n; i ++ ) 
				for (int j = 1; j <= n; j ++ )
					na[j][i] = a[j][w[i].second]; 
		}
		else {
			for (int i = 1; i <= n; i ++ ) for (int j = 1; j <= m; j ++ ) na[i][j] = a[i][j];
		}

那么它就会 WA#8

如果我都将列按最大值排序，再将前n列复制到新数组中（多出来也没事因为全是0），like this：

cin >> n >> m;
		for (int i = 1; i <= m; i ++ ) w[i].second = i;
		for (int i = 1; i <= n; i ++ ) 
			for (int j = 1; j <= m; j ++ ) 
				cin >> a[i][j], w[j].first = max(w[j].first, a[i][j]);
		sort (w + 1, w + m + 1, cmp);
		
		m = n;
		for (int i = 1; i <= n; i ++ ) 
			for (int j = 1; j <= n; j ++ )
				na[j][i] = a[j][w[i].second]; 
		

那么就AC了

这是啥原因啊我太菜看不出来